This invention relates to improvements in an injection port structure for use with syringes, to manufacture of syringes with the improved injection port, and more particularly to improved means for preventing reuse of syringes.
The rapid spread of acquired immune deficiency syndrome (AIDS) among intravenous drug users has created an urgent need for syringes that cannot be reused. In many situations, injections are given to patients without carefully controlling access to syringes. The use of reusable syringes under those circumstances increases the risk of infection. An infection can occur whenever syringes that have been used previously, and which therefore are no longer sterile, are used to administer injections.
Of course, reusable syringes are suitable for administration of a vaccine or other injectable medicaments when the injections are performed by a professional staff in formal health care facilities. In a hospital environment, skilled personnel sterilize the syringe for reuse, refill the syringe with the appropriate medicament, and personally administer the injections. Furthermore, circulation of these syringes is managed and controlled.
However, there are times when it is necessary or more economical to administer injections outside a hospital environment. For example, it may be necessary to give injections to a large number of individuals over a short period of time, patients may be located in a developing country or in an area without convenient access to a hospital or medical personnel, or it may be desirable to permit injections to be administered to a patient at his or her home or while he or she travels. Under these circumstances, it is very difficult to prevent misuse of the syringes. Furthermore, it is difficult to ensure proper sterilization of the syringes, particularly if medicaments are administered by non-professional personnel.
It is also important to develop an easy method of manufacturing a syringe having means for effectively preventing reuse of the syringe. Even though the use of disposable syringes reduces the risk of infection, it is not economically feasible to replace reusable syringes with disposable syringes unless the disposable syringes are made in a relatively inexpensive manner.
In view of the need for non-reusable syringes, various designs have been developed. For example, U.S. Pat. No. 3,667,657 describes a syringe having a knife which cuts the syringe wall to prevent reuse, while U.S. Pat. Nos. 3,951,146 and 3,998,224 disclose similar self-destructing syringe systems. A single-use syringe as described in U.S. Pat. No. 3,890,971 includes permanently-lockable plunger and slidable needle cap mechanisms.
Additionally, various valve designs have been developed for use with different syringe systems. For instance, U.S. Pat. No. 4,936,830 discloses a prefilled syringe having a one-way ball valve which only allows communication of the compartment containing the substance to be injected with the needle during injection. U.S. Pat. No. 4,952,206 describes another single-use syringe having an expandable plug which expands to engage a conical washer against an opening to prevent flow.
However, single-use syringes that have been developed suffer from various drawbacks, such as being expensive to manufacture, or being so bulky that the syringes are inconvenient to ship and store. Moreover, some known syringe designs are difficult to aspirate.
In order to ensure proper administration of an injection, it is important that the syringe be designed to allow aspiration to verify proper placement of the needle in the patient. Trained medical personnel confirm whether a needle is or is not in a blood vessel by aspirating prior to injection of a medicament. In aspiration, a negative or suction pressure causes the needle to draw material into the syringe from the patient. The person administering the injection then visually examines the syringe to see if any blood has been drawn into the syringe through the needle. If, for example, the injection should be administered intravenously, the presence of blood after aspiration indicates proper placement of the needle.
It is difficult to design a single-use syringe accommodating aspiration. Disposable syringes that contain a prefilled vaccine delivery system typically have a squeezable body portion or other elastic receptacle. In these syringes, a positive pressure is applied on or by the receptacle to force the medicament out through the needle. In order to perform aspiration, however, a negative pressure is applied to the receptacle. Unfortunately, the negative pressure needed to aspirate the syringe also may be used to reform the elastic receptacle, allowing the syringe to be reused.
In view of the need for an inexpensive and easy way to manufacture syringes that are difficult to reuse, but which can be used to perform aspiration, a syringe was developed as described in U.S. Pat. No. 4,955,871 to Thomas, the disclosure of which is hereby incorporated by reference. The Thomas syringe is provided with a reservoir for storing medicament and expelling it into the needle. The reservoir of the Thomas syringe provides for an "oil-can type" of flexing action.
In the Thomas syringe, the reservoir is formed by two sheets of thermoplastic material having expanded central portions forming a pair of compressible, convex domes. A connecting member spaces apart the domes. In response to complete compression of both of the central portions together, the reservoir substantially collapses and each of the domes becomes concave. This oil-can type action prevents the reservoir from being reformed and makes it difficult to reuse the syringe. However, after partial compression of the central portions together and partial collapse of the reservoir, upon removal of the compressing force the central portions expand to reform the reservoir and draw fluid into the reservoir, thereby aspirating a hypodermic needle.
It has now been found that the Thomas syringe can be reused with difficulty by one of two techniques. First, the oil-can action of the reservoir of the Thomas syringe can be overcome by inserting the needle of a used Thomas syringe into a pressurized container of the desired injectable material, whereupon the pressure blows the reservoir walls apart and fills it with the desired material for injection. Second, the Thomas syringe can be reused by putting the desired material into a Luer syringe, removing the needle from a used Thomas syringe, inserting the tip of the Luer syringe into the nozzle or port cylinder of the Thomas syringe, and injecting the desired material.